This invention relates in general to an improved encapsulated measuring device for large measuring lengths built up from a plurality of segments, and more particularly to such a measuring device comprising a protective housing and a scale with differing expansion coefficients, and a scanning unit.
In encapsulated longitudinal measuring systems the measuring scale is often subject to deformation caused by differential thermal expansion between the housing and the scale in response to temperature changes. For cost reasons, the housing generally is produced from aluminum. On the other hand, the scale generally is made of glass or a steel tape, and both glass and steel have expansion coefficients which greatly differ from that of the aluminum housing. In the measuring systems of the prior art the measuring scale is, therefore, often mounted to the housing by a resilient intermediate layer. The resilient intermediate layer reduces the transmission of distorting forces to the scale in the event of differential longitudinal expansion between the scale and the housing due to temperature fluctuations.
However, for reasons of production engineering it has heretofore been deemed impossible to manufacture the scale and the housing in self-contained segments of any desired length. Until now, a measuring device built up of several separate segments has been regarded as impractical due to unacceptably large errors produced at the junction between adjacent segments.